The present invention relates to a hydrophilic article having an outermost hydrophilic film, for uses in various fields such as of architectural and automotive window panes and mirrors.
In recent years, there have been proposals to form photocatalytic films on various substrates for providing stain resistance, deodorizing property, antibacterial property, hydrophilicity, and the like. For example, Japanese Patent First Publication JP-A-5-253544 discloses a method for producing a platelike member having a function of deodorization. In this method, a glaze (binder) layer is formed on a tile substrate. Then, a fine powder of anatase-type TiO.sub.2 in the form of sol is applied to the glaze layer. Then, the glaze layer is melted by heating and then solidified by cooling. With this, part of the TiO.sub.2 fine powder is exposed on the glaze layer. JP-A-7-232080 discloses a multifunctional material having a substrate, a binder layer formed thereon, and a photocatalytic layer made up of photocatalytic particles and filler particles for binding together the photocatalytic particles. It is disclosed therein that the photocatalytic particles may be made of TiO.sub.2, ZnO, SrTiO.sub.3, Fe.sub.2 O.sub.3, CdS, CdSe, WO.sub.3, FeTiO.sub.3, GaP, GaAs, RuO.sub.2, MoS.sub.3, LaRhO.sub.3, CdFeO.sub.3, Bi.sub.2 O.sub.3, MoS.sub.2, In.sub.2 O.sub.3, CdO, and SnO.sub.2. It is further disclosed that the filler particles are preferably made of metals such as Sn, Ti, Ag, Cu, Zn, Fe, Pt, Co, Pd and Ni and oxides of these metals. JP-A-9-59042 discloses a transparent substrate having an antifogging coating thereon. This coating is made of a mixture of a medium having a refractive index of less than 2 and titania particles having an average crystal particle diameter of not larger than about 0.1 .mu.m. It is known, when a photocatalytic titania film is directly formed on a Na.sup.+ -containing glass (e.g., soda-lime glass) substrate, sodium ions and alkali metal oxides may diffuse from the glass substrate into the photocatalytic film. With this, the photocatalytic activity of titania may be damaged. In view of this, there have been several proposals for forming a metal oxide interlayer under a functional film in order to prevent migration of sodium ions from a substrate (e.g., soda-lime glass) into the functional film. For example, JP-A-4-182327 discloses a functional glass plate having a Na.sup.+ -containing glass substrate; an ultraviolet-absorbing functional film containing ZnO and having a thickness of at least 0.5 .mu.m; and an undercoat layer (interlayer) interposed between the glass substrate and the functional film. This undercoat layer is made of a metal oxide such as SiO.sub.2, SiO.sub.2 -TiO.sub.2 or SiO.sub.2 -ZrO.sub.2. JP-A-7-315880 discloses a glass plate intended to be used as a touch panel that is superior in visibility. This glass plate has a transparent glass substrate, a first SiO.sub.2 film formed on the substrate, a second TiO.sub.2 film formed on the first film, and a third SnO.sub.2 transparent conductive film formed on the second film. The third film has a resistance of 0.5-1.5 K .OMEGA./.quadrature.. JP-A-8-190088 discloses a coated glass article having (a) a transparent glass substrate containing alkali metal ions; (b) a barrier layer formed on the glass substrate, for preventing diffusion of the alkali metal ions; and (c) a metal-containing coating formed on the barrier layer. The barrier layer has a thickness of not greater than 120 .ANG. and is made of a metal oxide selected from zirconium oxide and titanium oxide. The metal-containing coating is made of a conductive metal oxide selected from indium oxide, tin oxide, indium/tin oxide, and zinc/aluminum oxide.